Sounds like they put a SAND base underneath and its washing out from erosion. Either that or the base wasn't compacted good enough before adding...
PattciMkcrMember since 02/06/10
I would scuff the surface with 300 grit paper and apply a good name brand oil stain block primer. You can apply latex paint over the oil primer ...
If water leaks in anywhere, it'll follow underneath the flooring and it seems that you won't be able to tell where it came in.